This invention relates generally to pipeline padding machines and more particularly concerns padding machines which remove stones and other debris from excavated earth and return relatively clean soil into the excavation around a pipeline.
Most pipeline padding machines are laterally cantilevered from a tractor or other carrier with the padding machine positioned over the excavation or ditch containing the pipeline to be covered. As the tractor travels substantially parallel to the ditch, the padding machine traverses the length of the ditch and pipeline. This type of padding machine has many disadvantages.
One disadvantage is the limited size of the padding machine due to the cantilevered mounting arrangement. Reduced size results in reduced volume capability because volume is primarily a function of the surface area of the screen apparatus used to sift the earth. This disadvantage can be somewhat mitigated by the use of several tiers of vibrating screens, but this solution also increases the vertical profile of the machine which is itself undesirable. For example, some cantilevered padding machines discharge material from ten or more feet above the coated pipeline and the gravity accelerated velocity of the material from this height can damage the coating on the pipe.
The positioning of the padding machine over the ditch and adjacent to the carrier during the padding process is another disadvantage of the cantilever arrangement. In this relationship, heavy material is frequently deposited on top of the pipeline before it is sufficiently covered with fine material to protect the pipe. Therefore, the pipe may be damaged during the padding process.
The cantilevered arrangement also requires a clear pathway for the carrier parallel to and very close to the ditch to be filled. This is very impractical in difficult terrain conditions in which natural obstacles and variations in grade often obstruct the path of the carrier.
Feeding excavated earth into a cantilevered padding machine also presents a problem. Since the padding machine is over the ditch and directly adjacent to the carrier, access to the perimeter of the hopper which feeds excavated earth to the vibrating screen of the padding machine is quite limited. Any delay in the feeding process translates into a further reduction of the volume of clean earth returned to the ditch by the machine.
Another disadvantage of the cantilevered padding machine which emanates from its size limitations in conjunction with its location over the ditch is the inability of the unit to dispose of heavy materials not returned to the ditch at a distance far enough from the ditch so as not to interfere with padding or other work proximate the ditch. Furthermore, since the carrier is adjacent to the padding machine, it is extremely difficult to dispose of heavy materials anywhere other than along the edge of the ditch opposite the carrier.
One attempt to resolve some of these difficulties uses a towed padding machine which travels alongside of the ditch in a suspended arrangement beneath a rolling frame. This arrangement introduces many new problems. The mechanics and costs of suspending the enormous weight of the padding equipment beneath the frame limits the size of the machine and the surface area of the screen and therefore the volume of earth deliverable to the ditch. To conserve some space, the hopper which feeds the padding machine is mounted externally of the suspension structure, requiring another conveyor to transfer material from the hopper to the screen. Furthermore, since the hopper is external to the support structure and the machine, it can only be fed from one side.
Another type of padding machine is self-propelled and self-loading. As it travels, it plows up earth in front of it and conveys it upwardly and rearwardly to the padding equipment. This machine can only operate if moving in a forward direction and, typically, requires several passes along a given section of ditch to deliver sufficient material to pad a pipeline.
Accordingly, it is an object of this invention to provide a padding machine which is not cantilevered from its carrier. Another object of this invention is to provide a padding machine capable of distributing a high volume of padding material. And it is an object of this invention to provide a padding machine with a low velocity delivery system. A further object of this invention is to provide a padding machine which will deliver fine padding materials to a pipeline at a significantly greater distance ahead of the delivery point of relatively heavy padding materials than has been heretofore possible. It is also an object of this invention to provide a padding machine which facilitates the disposal of heavier materials either into the ditch, adjacent to the ditch or at distances from the ditch greater than heretofore possible. A related object of this invention is to provide a padding machine that will permit the padding machine and its carrier to operate at greater distances from the ditch than heretofore possible. A further object of this invention to provide a padding machine capable of traversing difficult terrain without interruption of the padding process. And it is an object of this invention is to provide a padding machine that can be used to stockpile fine materials.